The present invention relates to a filtering device for an injection device, and more particularly to a filtering device which provides for the introduction of filtered fluid into the injection device and subsequent injection of same into a patient or dispensing device without the necessity of having to remove and change needles between the drawing of fluids into the syringe and the injection of same.
One type of prior art filtering device for medical injection devices uses a first needle attached to the end of a syringe which has as an integral part thereof a filter medium, generally located adjacent the base of the needle when it is attached to the syringe, for the drawing of fluid through the filter needle and introducing same into the syringe. After the fluid has been aspirated through the filter needle, the needle with the filter is then removed and a second new needle is attached prior to injection of the fluid in the syringe into the patient or animal, or into a dispensing device. This product and arrangement has many objections, one of which is the fact that it requires a second needle and a product manipulation which has the potential of breaking sterile conditions. That is, with this arrangement one needle must be removed and replaced with a second needle, thus breaking or interrupting the supposedly sterile fluid path (i.e. between the needle and the syringe). Further, one of the greatest dangers with this type of arrangement is that the practitioner will forget to change needles and thus possibly inject into the patient a bolus or mass of particulates which have accumulated on the filter within the needle. For this latter reason, most hospitals have not allowed the use of filter needles outside the pharmacy.
Another type of product which has been used in the past comprises a filter tube which comprises a plastic tube having a hub portion with the filter medium therein. The hub is attached to the syringe and fluid is aspirated through the hub (where it is filtered) into the syringe. The filter tube is then removed and a needle attached to the syringe for subsequent injection of the fluid to the patient or into an intravenous bottle. This arrangement and product also has several disadvantages, among which include the fact that the filter tube must be removed and a needle attached before fluid can be injected. Such a manipulation can easily result in the breaking of a sterile technique or conditions in the fluid path. Still further, this arrangement requires that a needle be made available as a separate item of attachment.
A still further product which has been used in the past combines a needle with a second removable hub containing the filter, the hub being located at the end of the needle remote from the syringe. After aspirating the fluid through the needle/filter hub assembly and into the syringe, the practitioner is then required to disassemble the filter hub from the needle and the syringe, and then connect the needle to the syringe. In addition to the obvious manipulation which is required with this product and arrangement, there is also the potential for the needle to be contaminated with particulates.
Another device of the prior art is disclosed in U.S. Pat. No. 4,180,071 to Oiwa for a "Device for Withdrawing Injection Solutions", which is particularly adapted for use with solution containing ampuls which generally contain a solution sufficient for one injection only and which ampuls include a neck which is adapted to be cut and broken off to provide access to the solution therein or for withdrawing same into the syringe. In the arrangement disclosed in this reference, there is provided a tube whose length is such that when it is intimately fitted at its one end to the base portion of an injection needle, a filter medium, packed in the other or forward end of the tube, will be positioned slightly in front of the tip of the needle. The filter medium, which is disclosed as comprising a mass of fine fibers of polyester, polypropylene, polyamide or the like, is packed in the forward end of the tube and retained thereinplace by means of internal projections at each of the opposite ends of the portion of the filter medium to render the inserted filter medium somewhat retainable by the projections. In this arrangement, the portion of the tube around the filter medium is compressed by means of hot pressing or by permanently deforming the tube so that the filtered medium eventually has a multiplicity of pores ranging from preferably 3 to 5 microns in diameter. In use, the tube with the filter medium therein is placed over the base portion of the injection needle and the front end of the tube is then immersed in a solution in the ampul and the solution then withdrawn into the barrel of the syringe in a usual fashion. Because of the vacuum produced in the tube in this action, the solution is caused to flow into the needle through the filter medium which serves to filter out glass fragments contained in the ampul. Upon completion of the withdrawal of the solution, the tube is then removed from the needle base portion to provide an injection in the usual manner.
While such an arrangement overcomes some of the above-noted problems of the other prior art, the particular device and arrangement shown in U.S. Pat. No. 4,180,071 also possesses a number of disadvantages. For example, the particular filter medium used in this reference comprises an unsupported mass of fibers which are compressed to provide a pore size ranging from 3 to 5 microns in diameter. These fibers can become dislodged from their position in the forward end of the tube and perhaps even contaminate the end of the needle, which as can be appreciated is very disadvantageous. Furthermore, it is not possible with such an arrangement to provide for pore sizes ranging down to as little as 0.22 microns in diameter, the general accepted limit for providing a completely sterilized filtering as generally contaminating organisms and particles are generally of a greater size than 0.22 microns in diameter. Still further, the arrangement as disclosed in the Oiwa reference is not applicable for use with closed vials of solution which contain a number of doses of fluid to be injected as such vials are generally provided with rubber stoppers to maintain the sterile conditions within the vial and which rubber stoppers are designed to be pierced with a needle cannula to provide fluid communication with the solution in the vial; rather, the arrangement in the Oiwa reference requires an openable ampul. (It should be noted that the tapered end of the tube in the Oiwa arrangement does not comprise a needle cannula).